Introduction: Meningitis remains a major global public health concern, ranking among the most lethal infectious diseases and potentially causing brain injury if not promptly diagnosed or treated. Analyzing mortality trends by causative agent in Brazil helps identify patterns, assess the impact of prevention strategies, and guide effective health policies and clinical practices. Methods: This retrospective descriptive study used SINAN data from 2015 to 2024, stratified by etiology and organized into time series to identify trends. Results: From 2015 to 2024, viral meningitis — the most prevalent form in Brazil — decreased in total cases but showed higher lethality, rising from 113 deaths among 7,183 cases (1.6%) to 41 deaths among 1,767 cases (2.3%). Meningococcal meningitis followed a similar pattern, with lethality increasing from 38.1% (388 cases) in 2015 to 39.7% (78 cases) in 2024. Pneumococcal and Haemophilus influenzae meningitis also declined in incidence but had rising lethality (12.1% to 15.3% and 16.8% to 22.2%, respectively). Tuberculous meningitis remained highly lethal, from 55 deaths among 347 cases (15.9%) in 2015 to 21 deaths among 151 cases (13.9%) in 2024. Meningitis of unspecified etiology remained frequent, decreasing from 2,499 to 934 cases, with lethality dropping from 10.9% to 8.7%. Discussion and Conclusion: The results show a concerning pattern: meningitis lethality in Brazil has increased across several etiologies despite a reduction in overall cases. This discrepancy suggests that current prevention and control measures reduce transmission but have limited impact on disease severity and outcomes. Possible contributing factors include delayed diagnosis, gaps in healthcare access, antibiotic resistance, and limited availability of advanced care in some regions. These elements may lead to late treatment initiation, increasing the risk of neurological complications and death. Strengthening Brazil’s healthcare response through faster, more accurate diagnostics, timely therapy initiation, and broader access to effective antimicrobials is essential. Enhanced management strategies to prevent brain injury are particularly critical, as the rise in lethality likely reflects not only treatment delays but also increased neurological damage among survivors.